net: macb: Add TAPRIO traffic scheduling support

Implement Time-Aware Traffic Scheduling (TAPRIO) offload support
for Cadence MACB/GEM ethernet controllers to enable IEEE 802.1Qbv
compliant time-sensitive networking (TSN) capabilities.

Key Features:

1. Enhanced Scheduled Traffic (ENST) Register Management
   - Per-queue ENST registers: ENST_START_TIME, ENST_ON_TIME, ENST_OFF_TIME
   - Centralized control via ENST_CONTROL for gate enable/disable
   - Infrastructure enhancements:
     * Extended macb_queue structure with ENST timing control registers
     * Mapped ENST register offsets into queue management framework
     * Introduced macb_queue_enst_config for per-entry TC configuration
   - Timing conversion utility:
     * enst_ns_to_hw_units(): Converts nanoseconds to hardware units
     * Timing values are programmed as hardware units based on link speed
     * Conversion formula: time_bytes = time_ns / divisor
     * Speed-specific divisors: 1Gbps=8, 100Mbps=80, 10Mbps=800
   - Hardware limit utility:
     * enst_max_hw_interval(): Returns max interval for given speed

2. TAPRIO Configuration via "tc qdisc replace"
   - macb_taprio_setup_replace(): Configures TAPRIO hardware offload
   - Parameter validation checks performed:
     * TC entry limit validation against available hardware queues
     * Base time non-negativity enforcement
     * Speed-adaptive timing constraint verification
     * Cycle time vs. total gate time consistency checks
     * Single-queue gate mask enforcement per scheduling entry
   - Programming sequence:
     * GEM doesn't support changing ENST registers if ENST is enabled,
       hence disable ENST before programming
     * Atomic timing register configuration (START_TIME, ON_TIME, OFF_TIME)
     * Enable queues via ENST_CONTROL

3. TAPRIO Cleanup via "tc qdisc destroy"
   - macb_taprio_destroy(): Safely removes TAPRIO configuration
   - Restores default queue behavior
   - Cleanup steps:
     * Reset TC state
     * Disable ENST
     * Clear timing registers
     * Ensure atomic updates with locking

4. Traffic Control Offload Infrastructure
   - macb_setup_taprio(): TAPRIO command dispatcher
     * Verifies hardware support
     * Handles runtime suspend state
   - macb_setup_tc(): TC_SETUP_QDISC_TAPRIO entry point
   - Supports REPLACE and DESTROY operations

Tested on Xilinx Versal platforms with QBV-capable MACB controllers.

Signed-off-by: Vineeth Karumanchi <vineeth.karumanchi@amd.com>
Link: https://patch.msgid.link/20250814071058.3062453-2-vineeth.karumanchi@amd.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>